Reverse osmotic concentration of aqueous propionic acid and citric acid solutions were carried out using composite membrane PEC-1000 supplied from Toray Co. Ltd.,
Separation of propionic acid and citric acid, and flux through the membrane were measured under the following conditions : concentration of propionic acid, 2.28, 4.67, 9.25, 12.3wt%, concentration of citric acid, 2, 4.3, 9, 12.3wt%, operating pressure, 2.94, 3.92, 5.49, 6.86Mpa. The measured separations of propionic acid were always above 94% and those of citric acid above 99.95%.
An analysis of data with Spiegler-Kedem's transport model shows that the value of reflection coefficient σ, soulute and hydraulic permeabilities ω and Lp for propionic acid were 0.988, 2×10-11, 8.15×10-8, (mol/m2 pa. s), respectively, and those for citric acid 1.0, . 033×10-11, 8.52×10-8 (mol/m2pa. s) respectively.
Energy and membrane area required were calculated to concentrate dilute propionic acid and citric acid solutions by reverse osmosis. The energy per one kilogram of concentrated propionic acid is propotional to pressure difference and depends on the final concentration and concentration polarization, and found 0.3 and 0.7 kwh/kg-PAc at 5 and 10 MPa respectively to concentrate up to 14.7wt% from 0.5wt%. The energy of concentrated citric acid is proportional to pressure difference and independs on the concentration polarization. The area for two solutions are inversely propotional to operating pressure, and found to be 0.2-0.9m2/ (kgPAc/day), 0.06-0.2m2/ (kgCAc/day).
